It's time to read and vote for your favorite article in the 2013 Write-Off Contest! The four finalist's articles are featured in the May 13 newsletter and can be found through this link. Hurry! Voting ends May 18.
Invasiveness is subjective; it can vary from zone to zone, and garden to garden. In general terms, invasive plants are characterized as such because they exhibit one or more of the following tendencies:
1. Rapid, unchecked growth (which may require certain conditions; under adverse conditions, the plant's growth may be moderate);
2. Spreading by seed into areas where the plant is not desired and/or cannot be contained;
3. Spreading by runners or roots, which choke out or crowd other desirable plants (whether native or cultivated); and/or
4. Causing harm to the environment (For example, water hyacinth cuts off waterways in warm climates; kudzu vine smothers out and kills vegetation, including mature trees.)
5. An adjective describing an autonomous quality found in plants we don't like. When plants we do like spread themselves around the garden, we tend to place the blame squarely on ourselves. See green thumb
'Naturalized' is another word for 'invasive'. The terms ‘invasive’ and ‘weed’ are emotionally charged and based on subjective assessments. Depending on place and time a so-called ‘weed’ can become desirable and is even cultivated by the nursery trade.
Note the current popularity of Joe Pye Weed, Eupatorium purpureum, and Orange Butterfly Weed, Asclepias tuberosis). Japanese Knotweed, Fallopia japonica, and Elderberry, Sambucus canadensis, which makes a very functional sun-or-shade blind or hedge where other plants fail. If the objective is to 'naturalize' a species to form a blind or border then you want a plant that is fast-growing and ‘invasive’.
In a class on invasive species ecology and management the heated argument on this definition came out with one that was the most useful when talking about the environment;
Invasive species- An organism (plant) transported out of its native range (usually by humans, rarer by nature) and which has spread/is spreading/is able to spread into natural areas in a new range.
This is in contrast to Aggressive plants, which show an ability to outcompete other garden plants but which fail to disperse and survive to reproduction in the surrounding native environment. Note this definition eliminates the subjectivity of invasiveness, but a plant's status also should place it in a geographical context (zone, habitat, pH, etc.)
invasive by rhizomatous roots as well as seed. crowds out dired plants and impossible to pull . grows abundantly and saps all fertilizer from desired plants. runs underground, including under concrete. dollar weed is charming compared to this!
invasive by rhizomatous roots as well as seed. crowds out desired plants and impossible to pull . grows abundantly and saps all fertilizer from desired plants. runs underground, including under concrete. dollar weed is charming compared to this!
"Invasive species" is legally defined in the US by Executive Order 13112 “ as "an alien [non-native] species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” "Non-native" will depend on the ecosystem in question. Economic and environmental harm are difficult and expensive to assess and quantify. Harm to human health is easier to pin down. I don't know how many of the plants on this site that are characterized as being invasive really fit the legal definition. Perhaps "can become a weed" might be more appropriate, using "weed" in the sense of being unwanted. Gardeners understand that term perfectly.
This plant is extremely invasive, and has established large stands along most of Cache Creek along side of tamarisk (salt cedar) and Arundo (giant reed) in the Central Valley, California. It has spread the entire length of the creek in less than one year. Please do not buy or plant this if you live in California, Southwest and possibly the Northwest.
Photo shows plumes of Ravenna grass along the creek.
AGGRESSIVE WEED--that is a plant that is in my yard that I don't want. That is my MY problem. I pull it and get rid of it. INVASIVE SPECIES--that is a plant that is in my yard or anywhere else, which has no native enemies, and which escapes through seeds, runners, or any other method, and threatens the very existence of native species, plants, birds, microbes, fungi, insects, amphibians, fish, humans, crops, etc. That is EVERYONE'S problem. CASE IN POINT--I used to have morels in my woodlot. Since the invasion of garlic mustard, the morels have disappeared. The invader killed the microbes in the soil necessary to the morels' survival. That is the demise of a native species on my little piece of property--but I am sure that the morels in the neighboring state forest have also disappeared. I have used every method I can think of to get rid of the garlic mustard, and I simply cannot keep up with the production of thousands of seeds each year. LESSON--if a plant is listed as invasive, don't plant it. Don't assume that it will stay put in your yard. Plants don't know about property lines. It has seeds, it will move. It has no natural enemies to limit it. That is not based on subjective plant likes and dislikes. That is objective fact and a real threat. And don't get me started about lemon balm--used to have six plants--now I have thousands--it kills off other plants, produces thousands of seeds--and has moved outside of my property line. So now I guess it is everyones problem.